1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system and to a method of manufacturing such a magnetic head.
2. Description of the Related Art
The recording systems of magnetic read/write devices include a longitudinal magnetic recording system wherein signals are magnetized in the direction along the surface of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in the direction orthogonal to the surface of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of implementing higher linear recording density, compared with the longitudinal magnetic recording system.
Like magnetic heads for longitudinal magnetic recording, magnetic heads for perpendicular magnetic recording typically used have a structure in which a reproducing (read) head having a magnetoresistive element (that may be hereinafter called an MR element) for reading and a recording (write) head having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head comprises a magnetic pole layer that produces a magnetic field in the direction orthogonal to the surface of the recording medium. The pole layer incorporates a track width defining portion and a wide portion, for example. The track width defining portion has an end located in a medium facing surface that faces toward the recording medium. The wide portion is coupled to the other end of the track width defining portion and has a width greater than the width of the track width defining portion. The track width defining portion has a nearly uniform width.
For the perpendicular magnetic recording system, it is an improvement in recording medium and an improvement in write head that mainly contributes to an improvement in recording density. It is a reduction in track width and an improvement in writing characteristics that is particularly required for the write head to achieve higher recording density. On the other hand, if the track width is reduced, the writing characteristics, such as an overwrite property that is a parameter indicating an overwriting capability, suffer degradation. It is therefore required to achieve better writing characteristics as the track width is reduced. Here, the length of the track width defining portion orthogonal to the medium facing surface is called a neck height. The smaller the neck height, the better is the overwrite property.
A magnetic head used for a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface mentioned above. The medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider slightly flies over the surface of the recording medium by means of the airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider. In a magnetic disk drive the magnetic head is aligned through the use of a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit centered on the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In a magnetic disk drive of the perpendicular magnetic recording system that exhibits a better capability of writing on a recording medium than the longitudinal magnetic recording system, in particular, if the above-mentioned skew occurs, problems are encountered, such as an occurrence of a phenomenon in which data stored on an adjacent track is erased when data is written on a specific track (that is hereinafter called adjacent track erase), or unwanted writing between adjacent two tracks. To achieve higher recording density, it is required to suppress adjacent track erase. Unwanted writing between adjacent two tracks affects detection of servo signals for alignment of the magnetic head and the signal-to-noise ratio of a read signal.
A technique is known for preventing the above-described problems resulting from the skew, as disclosed in U.S. Patent Application Publication No. US 2003/0151850A1 and U.S. Pat. No. 6,504,675B1, for example. According to this technique, the end face of the track width defining portion located in the medium facing surface is made to have a shape in which the side located backward in the direction of travel of the recording medium (that is, the side located closer to the air inflow end of the slider) is shorter than the opposite side. Typically, in the medium facing surface of a magnetic head, the end farther from the substrate is located forward in the direction of travel of the recording medium (that is, located closer to the air outflow end of the slider). Therefore, the above-mentioned shape of the end face of the track width defining portion located in the medium facing surface is such that the side closer to the substrate is shorter than the side farther from the substrate.
As a magnetic head for perpendicular magnetic recording, a magnetic head comprising a pole layer and a shield is known, as disclosed in U.S. Pat. No. 4,656,546, for example. In the medium facing surface of this magnetic head, an end face of the shield is located forward of an end face of the pole layer along the direction of travel of the recording medium with a specific small space therebetween. Such a magnetic head will be hereinafter called a shield-type head. In the shield-type head, the shield has a function of preventing a magnetic flux from reaching the recording medium, the flux being generated from the end face of the pole layer and extending in directions except the direction orthogonal to the surface of the recording medium. The shield also has a function of returning a magnetic flux that has been generated from the end face of the pole layer and that has magnetized the recording medium. The shield-type head achieves a further improvement in linear recording density.
U.S. Pat. No. 4,672,493 discloses a magnetic head having a structure in which magnetic layers are provided forward and backward, respectively, in the direction of travel of the recording medium with respect to a middle magnetic layer to be the pole layer, and coils are disposed between the middle magnetic layer and the forward magnetic layer, and between the middle magnetic layer and the backward magnetic layer, respectively. This magnetic head is capable of increasing components orthogonal to the surface of the recording medium among components of the magnetic field generated from the medium-facing-surface-side end of the middle magnetic layer.
Consideration will now be given to a method of forming the pole layer in which the end face of the track width defining portion located in the medium facing surface has a shape in which the side closer to the substrate is shorter than the side farther from the substrate as described above. It is frame plating that has been often used in prior art for forming such a pole layer. In a method of forming the pole layer by frame plating, an electrode film is first formed on a base of the pole layer. Next, a photoresist layer is formed on the electrode film. The photoresist layer is then patterned to form a frame having a groove whose shape corresponds to the pole layer. Next, plating is performed by feeding a current to the electrode film to form the pole layer in the groove. The frame is then removed. Next, the electrode film except a portion thereof located below the pole layer is removed. Next, an insulating layer made of alumina, for example, is formed to cover the pole layer. Next, the insulating layer and the pole layer are polished by chemical mechanical polishing (hereinafter referred to as CMP), for example. Through the polishing, the top surface of the pole layer is flattened, and the thickness of the pole layer is controlled to be of a desired value.
The foregoing method of forming the pole layer has a problem that, if the polishing is stopped at a level other than a desired level, the thickness of the pole layer is made other than a desired thickness and the track width defined by the length of the above-mentioned side farther from the substrate is thereby made other than a desired value.
U.S. Patent Application Publication No. US 2003/0151850A1 discloses a technique in which the end face of the track width defining portion in the medium facing surface is shaped to have a first portion and a second portion. The first portion continuously increases in width from an end thereof located on the air-inflow-end side toward the other end located on the air-outflow-end side. The second portion is located on the air-outflow-end side of the first portion and has a uniform width that is equal to the width of the end of the first portion on the air-outflow-end side. This technique is capable of reducing variations in track width.
However, the technique disclosed in this publication has the following problem. According to the technique, the pole layer is encased in a groove formed in an inorganic insulating film. The groove is formed by etching, and has a tapered portion and a portion having an inner wall orthogonal to the top surface of the inorganic insulating film. However, it is not easy to form the groove having these two portions in the inorganic insulating film by etching. U.S. Patent Application Publication No. US 2003/0151850A1 discloses that the two portions are formed by changing conditions for etching.
According to the technique disclosed in this publication, the top surfaces of the pole layer and the inorganic insulating film are flattened by CMP or etching. However, the rate at which polishing by CMP proceeds and the etching rate are different between the magnetic metal material making the pole layer and the inorganic insulating material making the inorganic insulating film. Typically, the rate at which polishing proceeds or the etching rate of the magnetic metal material is higher than that of the inorganic insulating material under the conditions suitable for polishing or etching of the magnetic metal material. Therefore, according to the technique disclosed in the above-mentioned publication, even though an attempt is made to flatten the top surfaces of the pole layer and the inorganic insulating film by CMP or etching, it is likely in practice that the top surface of the pole layer is made recessed more deeply than the top surface of the inorganic insulating film. It is therefore difficult to form the pole layer having a desired shape through this technique.
The above-mentioned publication also discloses a method of forming the pole layer as will now be described. In the method, first, a first magnetic film is formed on the inorganic insulating film and in the groove formed in the inorganic insulating film. Next, the first magnetic film is removed by CMP or etching, so that the top surface of the first magnetic film is recessed more deeply than the top surface of the inorganic insulating film. Next, a second magnetic film is formed on the first magnetic film and the inorganic insulating film. The top surface of the second magnetic film is then flattened to form the pole layer made up of the first and second magnetic films. However, this method has a problem that the number of steps is increased.
Reference is now made to FIG. 39 to describe a basic configuration of the shield-type head. FIG. 39 is a front view of a portion of the medium facing surface of an example of the shield-type head. The shield-type head comprises: the medium facing surface that faces toward a recording medium; a coil (not shown) for generating a magnetic field corresponding to data to be written on the medium; a pole layer 316 having an end face located in the medium facing surface, allowing a magnetic flux corresponding to the field generated by the coil to pass, and generating a write magnetic field for writing the data on the medium by means of the perpendicular magnetic recording system; a shield layer 320 having an end face located in the medium facing surface and having a portion located away from the medium facing surface and coupled to the pole layer 316; and a gap layer 318 provided between the pole layer 316 and the shield layer 320. In this example the pole layer 316 is disposed on an insulating layer 314. An insulating layer 317 is provided around the pole layer 316. The pole layer 316 and the insulating layer 317 have flattened top surfaces on which the gap layer 318 is disposed. The shield layer 320 is further disposed on the gap layer 318.
The end face of the pole layer 316 located in the medium facing surface has a shape of trapezoid in which the side closer to the gap layer 318 is longer than the opposite side.
Problems of the shield-type heads such as the one shown in FIG. 39 will now be described. In FIG. 39 the physical track width PTW is determined by the width of a portion of the end face of the pole layer 316 located in the medium facing surface, the portion being in contact with the gap layer 318. However, a magnetic flux 321 starting from the pole layer 316 across the gap layer 318 and reaching the shield layer 320 extends wider than the physical track width PTW. Consequently, the effective track width ETW is greater than the physical track width PTW. For example, if the physical track width PTW is 0.12 micrometer (μm), the thickness of the pole layer 316 is 0.3 μm, and the thickness of the gap layer 318 is 50 nanometers (nm), the effective track width ETW is greater than the physical track width PTW by no less than 0.08 to 0.12 μm, according to conventional devices.
If the effective track width ETW is much greater than the physical track width PTW as described above, problems arises, such as adjacent track erase and unwanted writing performed between adjacent two tracks. If the physical track width PTW is reduced to reduce the effective track width ETW, such problems arise that it is difficult to control the physical track width PTW and that the overwrite property suffers degradation.
If the thickness of the gap layer 318 is reduced, it is possible to suppress expansion in the direction of track width of the magnetic flux starting from the pole layer 316 across the gap layer 318 and reaching the shield layer 320. In this case, however, there arises the problem that the overwrite property suffers degradation.